I. Field of the Invention
The present invention relates to a process for molding three-dimensional moldings and to an apparatus for performing this process.
II. Description of the Prior Art
Wherever it is necessary to shape flat starting materials which cannot be exposed to compression and stretching actions due to their structure or composition, difficulties are more particularly encountered during the molding process if the three-dimensional moldings to be produced have areas with a large final deformation or shaping. This problem is explained hereinafter relative to tangled-fiber fleece material, with particular reference to the production of moldings from binder-containing cellulose or lignocellulose mats.
In the production of moldings from tangled-fiber fleece blanks, which are softened and made deformable by heat action and the action of superheated steam, there is an increased risk of the fibrous fleece or non-woven fabric tearing during the molding process, because the fiber bonding union is largely removed by the heat treatment. If the moldings to be produced have considerable final deformations, it must be ensured that this tearing is prevented. This has hitherto been brought about by initially preshaping the thermally plasticized, flat tangled-fiber blank in cold premolding equipment, accompanied by the precompression thereof. Premolding has roughly the same three-dimensional configuration as the subsequent final molding (German Pat. No. 23 38 650). The required premolding means are, in part, very complicated, because they comprise male molds, covering, in each case, a shaping region with a specific degree of shaping, which are moved independently of one another in the sequence of the degrees of shaping from an open position into a pressing position. Thus, in this known process, apart from the expensive final molding press mold, it is necessary to have corresponding expensive molds for the premolding process.
In addition, separate presses are required for premolding, so that the total costs of the known procedure are further increased. In addition, for thermal plasticization, thermal energy is required, which is lost by the cooling of the molding following the premolding process.
It has therefore been proposed to make the overall process more economic in that, although carrying out premolding and final molding in two separate operating stages, they are performed using one plasticization stage, heat in successive travels in a single press and, consequently, without any intermediate cooling of the tangled-fiber fleece (German Pat. No. 30 28 242 and corresponding U.S. Pat. No. 4,378,265). This reduces the mold expenditure by a half mold, because e.g. the male mold for the premolding process can also be used for final molding and the aforementioned thermal energy loss is avoided. However, this process still requires precisely contoured premolding means having the same complicated construction as the final molding means which can only be used for a specific finished part so that their cost must be fully added to the final molding cost.